The NFL passer rating system is like the poetry of Ezra Pound: Everybody refers to it but no one knows what it means. The novice baseball fan may not know the value of a 3.27 Earned Run Average or a .456 On Base Average, but given time to observe and reflect, can easily figure them out. But what exactly does it mean even to experienced football fans that Peyton Manning’s league leading NFL passer rating is 99.0?

I’m told that the NFL passer rating isn’t all that difficult to figure out, but I’ve never seen the point of trying to learn it. For one thing, at least one of the statistics used in determining the NFL’s rating is useless, namely pass completion percentage. It matters little what percentage of a passer’s throws are caught; it only matters how far downfield they are completed. Ask yourself this simple question: Would you rather complete two of three passes for nine yards or one of three for 10? That’s all you need to know about the relative importance of pass completion percentage. If you want a good example, Houston’s David Carr leads the NFL in pass completion percentage at 68.6%, but his yards per throw average is slightly above mediocre, 6.23.

There’s a much simpler method for rating passers that is not only better at indicating effectiveness but offers an easily understandable statistic. I call it Adjusted Yards Per Pass, and you can figure it out in minutes over your Monday morning coffee at the office.

Adjusted Yards Per Pass utilizes just two numbers, but they’re the most important measures of a passer’s skill: yards per throw and interception rate. In the 1987 book “Football by the Numbers,” George Ignatin and I calculated the worth of interceptions by taking every game played in the NFL for 27 seasons from the inception of the 14-game schedule in 1961 through 1986. We factored in the yards gained on an average possession as well as yards gained on an average punt and punt return. For good measure, we also added in the number of yards gained on all interception returns.

The result was that the average interception in the NFL cost an offense 49.6 yards (and, conversely, was worth 49.6 yards to a defense). Four years later, with the assistance of coach T.J. Troupe, we analyzed the seasons 1987 through 1991 and found that the value of an interception had scarcely changed — from ’87 through ’91 an interception was “worth”49.7 yards. In 1999,Ignatin and I calculated all games for the four seasons from 1995–1998: still, 49.7. For ease in calculating our Adjusted Yards Per Pass, we rounded it to 50.

You know about interceptions, but you may not know as much about yards per pass, which is simply the yards a team gains through the air divided by the number of throws — not completions, but throws. Yards per pass is the single most important statistic in pro football, and the most reliable measure of a team’s strength on offense and defense. Every winning team in the modern NFL era has finished near the top of the food chain in yards per throw on either offense or defense, and usually in both.

By my estimation, around 80% of all NFL games since 1961 have been won by the team which, in the course of the game, averaged the highest yards per pass. Don’t take my word for it. Amaze your friends with this simple trick: On Monday mornings, have someone open the paper to the sports section and, without identifying the teams or the score, give you just two simple stats: the number of yards both teams passed for and the number of times they threw the ball. On average, you’ll be able to determine four out of five times which team won.

YPP is also the most underrated stat in pro football. Nearly every sports Web site includes it, but you have to seek it out because practically no one points out its significance. The biggest flaw in the NFL’s passer rating system is that it gives equal weight to pass completion percentage, which is almost meaningless, and YPP, which is vital.

With two weeks left to play in the 2006 season, below is a chart of the top 10 passers ranked by Adjusted Yards Per Pass with their NFL passer rating and rank for comparison.

Some observations:

• By our calculations, the Eagles’ Donovan McNabb and the Chiefs’ Damon Huard were on track to become the best passers in their respective conferences before they were injured. AYPP ranks them much higher than the NFL rating system.

• With all due respect to Chargers running back LaDainian Tomlinson, the Saints’ Drew Brees should have the inside track on this year’s MVP award — though after his Monday night performance, Peyton Manning is a close second. Cincinnati’s Carson Palmer was probably the second best candidate before the Bengals were stuffed by the Colts.

• The Cowboys’ Tony Romo — my nomination for the NFL quarterback whose name most sounds like a private detective in a Frank Sinatra movie — is easily the biggest surprise in the NFL this year. Romo’s yards per throw, 8.84, is nearly two full yards higher than that of the man he replaced, Drew Bledsoe. The switch makes Bill Parcells look like a genius, but the truth is he made the change out of desperation — if he had known how good Romo was and didn’t put him in sooner, he’d be an idiot.

• The Pats’ Tom Brady, 11th by the NFL’s method and by ours (AYPP 5.42),is headed for the worst season of his career. The Falcons’ Michael Vick (18th by the NFL, 17th by AYPP at 4.90) remains as mediocre. Chicago’s Rex Grossman (19th per NFL, 18th in AYPP at 4.89) was among the league’s top six passers for the first six games and has been one of the worst since then. No NFL quarterback this season has fallen so far as the Steelers’ Ben Roethlisberger. He was the first quarterback in modern NFL history to average 8.9 yards a throw in his first two seasons in the league; he’s currently averaging almost a yard and a half below his career average and has the highest interception percentage of all passers with 200 or more throws, 4.9%.

Mr. Barra is the author of “The Last Coach: A Life of Paul ‘Bear’ Bryant.”